This invention pertains to systems that are used in calibrating meters for purposes of assuring accuracy from the meter being calibrated. More specifically, the system enables the calibration of volumetric flowmeters, mass flowmeters, densitometers, and viscometers devoid of process connection.
It is desirable to perform a calibration on all meters prior to use in order to ensure accurate and reliable measurement data. The purpose of a meter calibration effort is to ascertain a flow calibration factor that will be used as a multiplier in correcting direct measurements from the meter under test. Coriolis meters, orifice meters, and positive displacement meters are known in the art as linear meters, i.e., the flow calibration factor is a constant with respect to flow rate. Other meters, including magnetic flow and vortex types, are nonlinear meters meaning that the flow calibration factor varies with respect to flow rate.
The calibration process typically is performed on a meter with process connections already attached as per a customer order. The meter is inserted into the calibration system having process connections that match those already attached to the meter. After insertion into the calibration system, the calibration process is performed. The most reliable calibration systems include gravimetric standards or master meter transfer standards used as flow rate references during the calibration process. The fluid used within the calibration system and the meter under test has precisely known intrinsic and extrinsic fluid properties, e.g., temperature, density, viscosity, and volume. The meter under test performs flow measurements on this fluid. These measurements are compared with the known fluid properties or flow rate reference to ascertain or validate a flow calibration factor or other calibration factors for the meter under test.
The problem with the above procedure is the requirement to have customer-specific process connections attached to the meter prior to performing the calibration. There are several drawbacks associated with this requirement.
One drawback is related to capital expenditure. In an effort to minimize warehouse inventory, meter manufacturers defer the process connection attachment step until a customer places an order. Furthermore, in an effort to reduce customer delivery lead-time, meter manufacturers locate customer service facilities around the world as near as possible to customers. As a result, since the calibration step currently follows the process connection attachment step, expensive calibration system hardware must be replicated in several facilities around the world.
Another drawback is the inability to test a meter for functional discrepancies immediately following meter assembly and prior to the meter proceeding through the process connection attach, calibration and shipping functions. With the current process, a discrepant meter would not be identified until it has completed its route through the customer service facility. Identifying the discrepant meter at the end of the process results in extremely high scrap costs and a delay in delivery to the customer.
For the reasons given above, a need exists for a meter calibration system with sufficient accuracy that enables calibration of meters devoid of process connections. Moreover, the system should be capable of calibrating both linear and nonlinear meters and should not reduce the current system""s performance or capabilities.
This invention overcomes the problems outlined above and advances the art by providing methods and apparatus capable of calibrating meters devoid of process connections. The apparatus are a calibration system and process connection adapters, where the system is operable for calibrating both linear and nonlinear meters at multiple flow rates, and is suitable for use with both gravimetric and master meter standard references.
One embodiment of the present invention is a process connection adapter used to fluidly connect a calibration system with a test meter devoid of process connections. The process connection adapter is an apparatus composed of a system mating portion, an intermediate portion, and a meter mating portion. The system mating portion is designed to physically match a connection on the calibration system. Typically this connection is in the form of a flange, sanitary fitting, union fitting, or some other type of sealing connection for piping. The intermediate portion transitions the flow area of the system mating portion to the flow area of the meter mating portion. The meter mating portion incorporates mechanical features to physically match a portion of the meter that would typically have a process connection attached to it. Depending on the connection type used by the system, a sealing component may be required to ensure that the interfaces between the process connection adapters, the calibration system, and the test meter are leak-free. Such a component could be an O-ring or gasket seal. During meter installation into the calibration system, the process connection adapters can either be secured to each of its mating members through bolts or other fittings or simply compressed as an assembly between hydraulic or pneumatic actuators.
The order fulfillment process begins by receiving a meter, devoid of process connection, from the manufacturing facility. Next, process connection adapters are attached on each end of the meter to form a test assembly. The test assembly is then mounted in the test bed by placing a portion of the test assembly on support structures integrated in the calibration system. Once the test assembly is fixed into the support structures, hydraulic or pneumatic actuators compress the calibration system connectors against the process connection adapters. This compression capability enables quick and easy insertion and removal of the test assembly while also ensuring a leak-free fluid path. Once the test assembly is inserted into the calibration system, the meter signal cabling is attached to the controller and the calibration process is started.
The basic meter calibration system includes a mechanism for supplying fluid to use in flow calibration measurements, a flow and density measurement reference, a controller for automating the system in order to optimize the accuracy or sensitivity of the measurements, and, of course, a meter under test. The flow measurements are used to ascertain or validate a flow calibration factor for the meter under test. The same principles apply for mass flow rate, volumetric flow rate, density, or viscosity calibrations.
The fluid supply mechanism can provide any fluid type; e.g., a liquid reservoir and a pump; a multiphase fluid including multiple immiscible liquid phases and gas; an attachment to a pressurized water supply, such as plant process fluids, a city water supply, artesian well, or gravimetric system; or a pressurized gas supply, such as natural gas, air, or plant process gases. For most meter calibrations, a constant-pressure source of water is the preferred supply mechanism.
The meter is operably configured, as described above, to receive fluid from the fluid supply mechanism. The meter under test is positioned in the flow piping between the fluid supply and either a scale, as in the case of a gravimetric system, or a master meter array as in a master meter system, described in U.S. Pat. No. 6,360,579 issued to DeBoom et al.
Once the calibration process is started, the meter under test provides flow measurement signals to a supervisory CPU-based controller. The controller adjusts valves leading to the meter for the purpose of controlling flow through the meter within the range of optimal measurement sensitivity corresponding to relatively low uncertainty for the meter. The controller interprets these electrical signals as flow measurement data and calibrates the meter under test using a flow calibration factor obtained from flow data.